| MadSci Network: Anatomy |
Suffice it to say that there is no process for counting all the cells in the human body. I cannot verify the source of the number in the original posting that is refered to here, 10exp14. However, I am certain that this, as well as the estimate of >7.5 trillion cells (7.5 x 10exp12) given at the Encylopedia Brittanica site below are just guesses based on some very rough extrapolations. Probably the best approach is to take a fragment of known weight from a tissue such as liver or brain; you would also need to know the weight of the entire tissue. By dissociating the fragment into a cell suspension and counting a sample of the cell suspension, one could arrive at a reasonable estimate for the total number of cells in that organ. (I'm ignoring the difficulty of obtaining human material for such a project.) My own guess, based on the knowledge that 10exp10 cells can fit comfortably in one hand, but that tissues consist of non-cellular material as well as cells, is that the correct number is between the two given above. The following site has many human body factoids, with interesting educational links: http://www.education-world.com/a_lesson/lesson065.shtml The treatment at the britannica site is interesting as well: http://www.britannica.com/bcom/eb/article/9/0,5716,42389+2+41468,00.html Finally, remember that the number of cells in the body is not static; a number of cell types (blood, skin and intestinal cells come to mind) are constantly cycling, with new cells replacing old. Thus, there may not be a single correct number, but rather a normal range.
Try the links in the MadSci Library for more information on Anatomy.